The invention relates to steering and thrust control systems for waterjet driven boats.
With a waterjet drive, seawater is drawn in through the bottom of the boat and ejected in a stream out the back. The reaction to this movement of water is the propulsive force that moves the boat. Near the back of the stream is a nozzle, which serves two functions. It accelerates the stream by reducing its diameter, and it can be turned from side to side to deflect the exiting stream to apply a component of side force on the aft part of the boat. The nozzle is to a jet what a rudder is to a boat equipped with conventional propellers. Both are typically connected to a steering wheel.
The aftmost portion of the jet, just behind the nozzle, is a device called a reversing bucket. Its function is to allow the operator to reverse some or all of the stream in order to stop or back up the boat. In normal underway operation the bucket is elevated above the stream and has no effect. When reduced forward thrust is desired the bucket can be lowered into the stream, forcing a portion of the flow through curved channels until it exits in a forward and slightly downward direction. When roughly half the stream is still streaming aft below the bucket and half is being reversed to a more forward direction (the neutral bucket position), an approximate balance point can be reached that results in approximately no forward or aft thrust on the boat. If the bucket is lowered to the full down position, nearly all the thrust is reversed and the boat should begin moving in reverse. The particular design of some reverse buckets (e.g., Hamilton waterjets), and the way the bucket interacts with the nozzle, permits a net thrust in any direction in the plane of the water""s surface. Side to side force is adjusted by nozzle position, and forward or aft force by bucket position.
A waterjet is either engaged and pumping water or disengaged and not pumping water. It does not ordinarily have a forward and reverse in the same manner as a conventional propeller. A transmission with reverse gear can be provided as a means of allowing the engine to run without engaging the jet and to allow for backflushing that results from reversing the drive shaft to the jet to clear an obstruction that may have been drawn against the jet inlet. Actual reverse thrust is accomplished with the jet engaged in the forward direction and the bucket lowered, similar in concept to the reversing arrangement on aviation jet engines.
Waterjet drives have numerous advantages, e.g., low draft, reduced noise, improved high-speed maneuverability. But they can make a boat difficult to control at slow speeds in tight quarters (e.g., when docking). The reason for this is that, heretofore, there has been no simple way to achieve zero thrust or zero side force. In a conventionally powered boat, zero thrust and zero side force are easily achieved, simply by putting the transmission into neutral, thereby bringing the propeller to rest. But with a waterjet, the only way to achieve zero thrust is to move the bucket to a position at which the net of the forward and reverse portions of the jet is balanced. That position can only be chosen approximately. It takes considerable training and experience for an operator to acquire a sense of what the waterjet drive is doing, to allow successful slow speed operation.
Waterjet drives also behave differently in reverse from propeller driven craft. Because the flow of water through the jet is always in one direction, deflection of the stream results in the same sideward force regardless of whether the boat is moving forward or in reverse. This is in contrast to a conventional rudder, whose effect on the stern of a boat is reversed depending on the direction of travel through the water. This difference in steering in reverse presents difficulties for new operators, who anticipate that steering direction will change when the boat is backing up.
To control movement of the bow of a boat, some boats are equipped with bowthrusters. Such a thruster is often installed in a tube that runs from side to side at the bow below the waterline. In the middle of this tube is a propeller that can thrust either way by reversing rotation. In smaller boats, this propeller is usually driven by an electric motor. The combination of waterjet and bowthruster can give a boat extraordinary maneuverability. Movement in any direction in the plane of the water""s surface is possible, even directly sideways. But, unfortunately, the operator is typically required to skillfully coordinate different controls simultaneously to take full advantage of this maneuverability. E.g., a foot pedal or left/right deflection of a hand-operated lever may be used to control the bowthruster, a steering wheel, to control the rear nozzle, and a throttle lever, to control speed.
Some very large waterjet driven ships have solved the zero thrust difficulty by controlling the waterjet with an inertial control system that senses applied thrust (e.g., using accelerometers), and adjusts the waterjet bucket position until a desired thrust level is achieved. When the operator desires a zero thrust level, the control system adjusts the bucket position until the inertial sensors detect zero applied thrust. This solution is too expensive for small boats (i.e., boats 75 feet or less in length).
We have discovered an improved method for controlling a waterjet drive that overcomes prior difficulties with low-speed handling of boats with waterjet drives. The invention has numerous advantages. It allows a relatively unskilled operator of a jet boat to quickly master low-speed control of the boat. In preferred embodiments, control of reversing bucket, nozzle, and bowthruster are combined in a single joystick in a manner that is surprisingly easy for an unskilled operator to master. By having the joystick return to a neutral position corresponding to balanced, neutral fore/aft thrust (and preferably also neutral port/starboard nozzle thrust), it is possible for the operator to reliably put the boat in neutral, something not readily possible in conventional waterjet boats. This control arrangement also overcomes the problem that waterjet drives tend to behave differently in reverse than conventional propeller driven craft.
In a first aspect, the invention features providing a bucket position sensor connected to the reversing bucket of a waterjet drive, and controlling the bucket in response to an output of the position sensor to enable the bucket to be automatically moved to a neutral thrust position.
One or more of the following features may be incorporated in preferred embodiments of the invention:
A joystick may be configured so that when the joystick is placed in its neutral-position the drive mechanism automatically moves the reversing bucket to the neutral thrust position.
A centering force can be provided in the joystick so that when released by the operator, the joystick returns to its neutral position and the thrust is returned to neutral.
The joystick can be configured so that rotation (or twist) of the joystick about a generally vertical axis controls rotation of the waterjet nozzle about its axis.
A nozzle position sensor may be connected to the nozzle, and provide control circuitry with a measurement of the position of the waterjet nozzle.
The joystick may have a centering torque that returns the stick to a zero rotation position when released by the operator. The control circuitry may be configured with the nozzle position sensor so that releasing the joystick and allowing it to return to the zero rotation position automatically causes the nozzle to return to a zero sideward force position.
The automatic zeroing of sideward force can be combined with the automatic zeroing of forward/reverse thrust, so that when the operator releases the joystick all propulsion forces on the boat are brought to zero.
A bowthruster can be controlled by left/right movement of the same joystick, so that leftward movement of the joystick produces a leftward movement of the bow of the boat and rightward movement of the joystick produces rightward movement of the bow.
The bucket position sensor, joystick, and control circuitry may be configured to provide at least two modes of operation, a first mode in which a follow-up relationship exists between forward/aft movement of the stick control member and up/down movement of the reversing bucket, and a second mode in which a non-follow-up relationship exists between forward/aft movement of the stick control member and up/down movement of the reversing bucket.
The nozzle position sensor, joystick, and control circuitry may be configured to provide a follow-up relationship between the rotation of the stick control member and rotation of the nozzle.
The electrical circuitry may be configured to provide both a docking mode and a power steer mode of operation, wherein in the docking mode of operation, the bucket position sensor, nozzle position sensor, and stick control member are configured so that both bucket position control and nozzle position control have a follow-up relationship to the respective movements of the stick control member, and wherein in the power steer mode of operation, the bucket position sensor, nozzle position sensor, and stick control member are configured so that bucket position control is non-follow-up and nozzle position control is follow-up.
In the power steer mode of operation, the electrical circuitry and stick control member may be configured so that rotational movement of the stick member produces less rotation of the nozzle than in the docking mode.
A trim adjustment control may be provided to permit the operator to adjust an offset between nozzle position and joystick rotation.
Hydraulic cylinders may be used to position the bucket and/or nozzle, and the components may be configured to provide two speeds of movement of the hydraulic cylinder, a high speed movement for use when the cylinder is more than a predetermined distance away from the position prescribed by the control circuitry, and a low speed movement for use when the cylinder is less than the predetermined distance.
Other features and advantages of the invention will be apparent from the following description of preferred embodiments, and from the claims.